Magnetic thin-film media, wherein a fine grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are generally classified as “longitudinal” or “perpendicular,” depending on the orientation of the magnetization of the magnetic domains of the grains of the magnetic material. In longitudinal media (also often referred as “conventional” media), the magnetization in the bits is flipped between lying parallel and anti-parallel to the direction in which the head is moving relative to the disc.
Perpendicular magnetic recording media are being developed for higher density recording as compared to longitudinal media. The thin-film perpendicular magnetic recording medium comprises a substrate and a magnetic layer having perpendicular magnetic anisotropy. In perpendicular media, the magnetization of the disc, instead of lying in the disc's plane as it does in longitudinal recording, stands on end perpendicular to the plane of the disc. The bits are then represented as regions of upward or downward directed magnetization (corresponding to the 1's and 0's of the digital data).
FIG. 1 shows a disk recording medium and a cross section of a disc showing the difference between longitudinal and perpendicular magnetic recording. Even though FIG. 1 shows one side of the disk, magnetic recording layers are usually sputter deposited on both sides of the non-magnetic aluminum substrate of FIG. 1. Also, even though FIG. 1 shows an aluminum substrate, other embodiments include a substrate made of glass, glass-ceramic, aluminum/NiP, metal alloys, plastic/polymer material, ceramic, glass-polymer, composite materials or other non-magnetic materials.
While perpendicular media technology provides higher areal density capability over longitudinal media, granular perpendicular magnetic recording media is being developed for further extending the areal density as compared to conventional (non-granular) perpendicular magnetic recording which is limited by the existence of strong lateral exchange coupling between magnetic grains. Granular structure provides better grain isolation through oxide segregation to grain boundary, hence enhancing grain to grain magnetic decoupling and increasing media signal to noise ratio (SNR).
A granular perpendicular magnetic layer contains magnetic columnar grains separated by grain boundaries comprising a dielectric material such as oxides, nitrides or carbides to decouple the magnetic grains. The grain boundaries having a thickness of about 2 Å to about 30 Å, provide a substantial reduction in the magnetic interaction between the magnetic grains. In contrast to conventional perpendicular media, wherein the longitudinal magnetic layer is typically sputtered at low pressures and high temperatures in the presence of an inert gas, such as argon (Ar), deposition of the granular perpendicular magnetic layer is conducted at relatively high pressures and low temperatures and utilizes a reactive sputtering technique wherein oxygen (O2), CxHy, and/or nitrogen (N2) are introduced in a gas mixture of, for example, Ar and O2, Ar and CxHy) Ar and N2, or Ar and O2, CxHy, and N2. Alternatively, oxide, carbide or nitrides may be introduced by utilizing a sputter target comprising oxides, carbides and/or nitrides which is sputtered in the presence of an inert gas (e.g., Ar), or, optionally, may be sputtered in the presence of a sputtering gas comprising O2, CxHy, and/or N2 with or without the presence of an inert gas. Not wishing to be bound by theory, the introduction of O2, CxHy, and/or N2 reactive gases, and oxides, carbides, and/or nitrides inside targets provides oxides, carbides, and/or nitrides that migrate into the grain boundaries, thereby providing a granular perpendicular structure having a reduced lateral exchange coupling between grains.
FIG. 2 illustrates a granular perpendicular magnetic recording medium design. Conventional seed layers are used to prepare and enhance crystal growth of the interlayers. Seed layers are normally amorphous (e.g., Ta and Ta alloys) and/or FCC materials (e.g., Cu, Au, and Ag).
The interlayers are normally Ru and Ru alloys which grow hcp <002> orientations to serve as templates for perpendicular growth of magnetic alloys. The interlayers have a total thickness of at least 200 Å.
Under conventional process conditions, the perpendicular media structure is not “rigid” enough to survive the sheer stress caused by hard particles. This results in physical mechanical damage and accompanying irreversible magnetic damage and malfunction. In addition, the high cost of Ru makes thinner Ru-based layers desirable.